Often, an involuntary search is preceded by another form of search, the once-over by the urban myth known as the infallible drug sniffing dog. Old Bowser can be relied upon to find drugs anyplace the police want to find drugs. (Yes, the dogs can detect drugs, but they can be easily manipulated or tricked into "sensing" drugs where no drugs exist, at least prior to the roadblock stop.)
Go check it out! Be safe, and play smart if you are at a roadblock!